Techniques of transgenic and gene targeting in mice have been used widely to study in vivo functions of genes during development and adult life. Standard knockout and transgenic mice have been highly informative, but early embryonic lethality or complex phenotypes involving multiple tissues often obscure the roles of subject genes at later stages of development, in adults or in specific tissues. For example, many knockout mice of transcription factors and growth factors and their respective receptors exhibit ocular phenotypes (including the cornea), but embryonic lethality or premature death precludes the possibility of further examining the functions of such genes in adults. Mice derived from conditional expression of transgenes and tissue-specific gene ablation provide a means of circumventing certain limitations of conventional transgenic and gene targeting mouse models. This can be achieved by the use of tissue-specific promoter to drive the expression of Cre and rtTA in transgenic mice. For example, it has been demonstrated that K12 keratin gene (Krt1.l2) is solely expressed by corneal epithelium. Thus, Krt1.12 promoter would be excellent for the preparation of transgenic mice expressing Cre and rtTA, a technique that can be used to prepare mouse lines that have cornea epithelium-specific gene ablation and conditional expression of reporter genes such as growth factors, receptors, transcription factors, etc. Unfortunately, attempts to identify a functional Krt1.12 promoter in transgenic mice have proved fruitless. To circumvent this difficulty, in the proposed studies a knock-in strategy of gene targeting techniques will be used to prepare Krtl.12"c' (Specific Aim 1) and Krtl.12+I"TA (Specific Aim 2) mouse lines expressing Cre and rtTA in corneal epithelium, respectively. These mouse lines will be useful in preparing mouse lines for studies of altered genetic functions from the corneal epithelium-specific gene ablation and overexpression of reporter genes.